Tech Specs say 4 hour full-charge time..

When my iPod (Touch 5g) gets low on battery, I plug it in like most people do. However, it charges to "100%" in about 45 minutes. I find this very strange, because the tech specs for this device say it takes about 4 hours for a comple recharge. Normally this quick charging would be a plus, but I find that my iPod dies very quickly, moreso than it used to. I'm not sure if the battery percentage sensor is messed up, or if it's because of iOS 7... Does anyone else have this problem, and/or know what to do to fix it?